1. Field of the Invention
The present invention relates to a defroster for a refrigerator, and more particularly, to a defroster for an evaporator of a refrigerator for eliminating frost formed on the evaporator by causing calorific values to vary according to positions in the evaporator.
2. Description of the Prior Art
Cold air which circulates in a refrigerator and performs cooling and freezing actions is generated through heat exchange with a refrigerant in a heat exchange cycle of an evaporator of the refrigerator. Moisture absorbed into the cold air during the circulation of the cold air in the refrigerator adheres on a surface of the evaporator, which is in a relatively low temperature state, and is formed into frost thereon. If the frost grows and becomes ice with a thickness exceeding a certain thickness, the ice disturbs the flow of the cold air passing by the evaporator. This results in fatal hindrance to a heat exchange efficiency of the evaporator.
In order to solve the problem, a defrosting process is periodically performed at a predetermined time interval. Generally, such a defrosting process is carried out by operating a heater installed at the evaporator.
As shown in FIG. 1, a general evaporator 1 includes a refrigerant tube 2 which is arranged in a serpentine state in a vertical direction and through which a low-temperature and low-pressure refrigerant flows. A heater 4 is also arranged in the serpentine state in the vertical direction in the same manner as the refrigerant tube 2. The refrigerant tube 2 and the heater 4 are supported by supporting plates 5 provided at both the right and left ends of the evaporator 1. A plurality of heat radiation fins 6 are added to the refrigerant tube 2 between the supporting plates 5 so as to facilitate the heat exchange in the refrigerant tube.
Meanwhile, FIG. 2 shows the inner constitution of the heater. As shown in the figure, a heater tube 7 made of aluminum defines an external appearance of the heater 4. A hot wire 8 is wound at a predetermined interval within the heater tube 7. The hot wire 8 radiates heat when electric power is applied thereto, and is wound on an outer periphery of a core 9 and covered with an insulating cover 10. That is, the heater 4 is constructed in such a manner that the hot wire 8 wound on the core 9 and covered with the insulating cover 10 is disposed within the heater tube 7.
Crimped terminals 11 are provided at both ends of the heater tube 7 of the heater 4, and the hot wire 8 is connected to lead wires 12 provided on outer sides of the crimped terminals 11 and thus is supplied with electric power from the outside.
However, the aforementioned prior art has the following problem.
In the conventional heater 4, the hot wire 8 is wound at a uniform interval as a whole. Therefore, when the hot wire 8 radiates heat, an almost identical amount of heat is radiated from all regions of the heater tube 7.
However, frost with a uniform thickness is not always formed and grows throughout all regions of the evaporator 1. For example, it is apparent that a large amount of air comes into contact with a portion of the evaporator into which the air that has circulated in the refrigerator is introduced through a return duct, and a large amount of frost is thus formed and grows on the portion of the evaporator. On the contrary, a small amount of frost is formed and grows on outer portions of the supporting plates 5.
In spite of the different amounts of the frost formed on respective portions of the evaporator 1, if a uniform amount of heat is radiated throughout the heater 4, this causes a problem. That is, a portion where the large amount of frost is formed cannot be efficiently defrosted, and at the same time, heat from a frost-free portion is conducted to the inside of the refrigerator and thus it is likely that the temperature of the interior of the refrigerator may be substantially increased.
An object of the present invention is to provide a defroster capable of most efficiently performing a defrosting process with optimum electric power.
According to the present invention for achieving the object, there is provided a defroster for an evaporator of a refrigerator, comprising a refrigerant tube arranged repeatedly at a predetermined interval so as to allow a refrigerant flowing therein to evaporate and absorb heat from the surroundings; a plurality of heat radiation fins installed to be in contact with an outer periphery of the refrigerant tube for enlarging a heat exchange area; and a defrosting heater for generating heat to eliminate frost formed on an outer surface of the refrigerant tube and the heat radiation fins. Pitches of a wound hot wire provided in the defrosting heater are set to be different from one another at respective regions of the defrosting heater according to the amount of frost to be formed.
The pitch of the wound hot wire on an inlet side through which air that has circulated in the refrigerator is introduced for heat exchange toward the evaporator is preferably smaller than that on an outlet side through which the air leaves the evaporator.
The pitch of the wound hot wire at a portion of the defrosting heater by which air that has circulated in a refrigerating chamber of the refrigerator passes is preferably smaller than that at a portion of the defrosting heater by which the air that has circulated in a freezing chamber of the refrigerator passes.
The defrosting heater may be constructed by winding the hot wire around a core at the predetermined pitches, covering the hot wire wound around the core with an insulating cover, and inserting the covered hot wire and core into a heater tube.
The defrosting heater may be further provided with non-heating regions where heat is not radiated, by causing conductors to be connected in parallel with the hot wire.
With the constitution of the present invention, there are advantages in that maximum defrosting performance can be achieved with optimum electric power and heat generated during the defrosting process can be simultaneously prevented from being introduced into the interior of the refrigerator.